remote: update config files to note usage wrt systemd socket activation

remote: update config files to note usage wrt systemd socket activation

Certain libvirtd.conf settings are not honoured when using systemd
socket activation.

Certain systemd unit file settings must match those defined in
libvirtd.conf for systemd socket activation to work with systemd
version < 227, otherwise libvirtd cannot determine which inherited
FD to use for which service.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>